Gas turbines, when used for land use electrical power generation, are typically required for both 50 Hz and 60 Hz applications, depending upon power grid frequency. The costs involved in developing and producing machines for both frequencies are quite significant. For example, components for a turbine designed for each different frequency application are typically unique to that turbine. This results in higher investment costs for tooling and virtually no commonality of hardware as between the two turbines, which would beneficially impact turbine costs.
One approach commonly used for developing gas turbines for 50 Hz and 60 Hz frequency applications is simple geometric scaling of one design to a second frequency. Scaling is based on the principal that one can reduce or increase the physical size of a machine while simultaneously increasing or decreasing rotational speed to produce aerodynamically and mechanically similar compressors and turbines for the different frequency applications. Application of scaling techniques has enabled the development of turbines for both frequency applications which, while reducing development costs, still results in turbine components unique to the turbine for a particular frequency application. For example, components for a turbine designed for a 50 Hz application are scaled geometrically by the frequency ratio 50/60=0.833 to yield similar turbine performance at 60 Hz frequency. With this fixed geometric scaling, power output scales by the inverse square of the frequency, i.e., (50/60).sup.2 =0.694. Thus, a turbine sized at 50 Hz to provide a power output of 100 megawatts would, when geometrically scaled by a factor of 0.833, provide a power output of 69.4 megawatts at 60 Hz. More generally, there is a fixed relationship or ratio between output power at one speed and power output at another speed when turbine designs are geometrically scaled. The advantage of this scaling approach is that components sized at one frequency can be readily redesigned at the scaled frequency. However, the output of the turbine is fixed by the scale factor and thus one or the other of the turbines may not be optimum for a particular application. That is, market demands may require turbines for operation at different frequencies and the power output of one turbine at one frequency may not result in the desired output of the other turbine at the other frequency when the first turbine is geometrically scaled to afford the second turbine. Equally important, the components (hardware) for a base turbine for one frequency application have virtually no commonality with the components (hardware) of the scaled turbine for the different frequency application, resulting in increased tooling and component parts costs as well as other disadvantages.